Vacuum tube



H. A. SNOW VACUUM TUBE July 21, 1936.

Original Filed March 19, 1930 I 3mm Patented July 21, 1936 PATENT OFFICE C -I 'BE' Harold A. Snow, Mountain 'Lakea-N. J.,' assignor, 1 r

by mesne assignments, to-Radio'= Corporation of America, New York,

Delaware N.. Y.,'. a corporation of Original application March 19,v 1930, Serial 'No.

437,225; Divided and this application'March 10, 1931, Serial No.'521,577,- Renewed June 26, 1934 In Canada September 13, 1930 V This invention relates to vacuum or electronic tubes suitable for theamplification of modulated carrier waves; r 7 i This application is a division of my copending ll -ap'plication, Ser. No. 137,225, filed March 19, 1930- and; for a more extended discussion of the method of operation and the advantages of vacuumtubes of the poly-mu, orvariable mu'factor, type dis- 1 ,closed and claimed in this application, reference is-madetothe aforesaid application and'to the article by Stuart Ballantine and Harold'A. Snow in the Proceedings of-the Institute of Radio- Engineers, December, 1930, pages 2102 to- 2127,

- 1, Reduction of distortion and cross-talk in radio,

receivers by means of variable-mu tetrodes 1 'An object 'of the invention is to provide a vacuum tube of the type having two or more grid electrodes between the thermionic cathode and the plate in which'the electrodes are constructed and arranged'to produce a desired relation be--- tween the current flow; in one electrode circuit and the voltage on another electrode, for example,"

i be en plate current and control grid voltage. A -further object is to provide a tube ofthe type stated in which the control grid and another grid such as a; screen grid are so constructed that the space current path adjacent difierent parts of the cathode is characterized by substantially different mu factors and transconductance values. A furtherobject is to provide a, vacuum tube of the type statedhaving an equipotential cathode and injwhich the control grid has the form of a helicalwinding of non-uniform pitch. More specifically, 7 an object is to provide a vacuum tube of the type stated havingcoaxial cylindrical elements, and in which the control grid has the form of a helical winding of progressivelyfvarying pitch.

These and other objects or the invention will be apparent from thefollowing specification when }'Fig'." 1 isa perspective View of a vacuum tube embodying the invention, parts being broken away to; illustrate the construction of the control .grid, mg. 2 is an enlarged detail view of a control grid such as shown in Fig.1, and i j Fig; .3, is a diagrammatic 'view illustrating another embodiment of the invention. 'In Fig. 1, the invention 'is illustrated as e11 bodied in a form of vacuum tube known common ciaIIy as a-screen'grid tube having a separate heater for energizing an equal-potential cathode. As is well known, this particular type of tube comprises an evacuated envelope l enclosing a cathode 55 2 heated by a resistance heater (not shown) taken with the accompanying drawing, in which" withinthe cathode, an inner or control grid G1, a screengrid G2, a plate P and an outer screen S. Except for the novel'construction of the control grid G1 and of the screen grid G2, the several elenients of the tube and their physical arrange- 5 ment may be substantially the same as that employed inthe present commercial tubes.

In tubes of this general type, the control grid G1 comprises a helical winding, of uniform pitch,

supported by one or more wires which extend 10 parallel to the axis of the cathode 2.

In accordance with the present invention, the desired operating characteristics of the tube, as explained in my copending application and the aforesaid publication, are in part obtained by making the control grid winding of non-uniform pitch. As shown in Fig.2, the control grid G1 may take the form of a winding or coil 3 of progressively varying pitch which is supported by parallel wires 4. a As the control grid portions of gre'ater pitch exercise a lesser rate of control of the electron stream than the control grid portions of lesser pitch, the inn factor of a tube with such a control gridis relatively low at the area of the cathode adjacent the control grid portions of 25 greater pitch, and both the space current and the transconductance of the space current path from the low mu area of the cathode are relatively high. I Greaterfreedoni'of design is permitted by altering the geometry of more than one of the electrodes. For example, with a control grid of variable pitch; I find it of advantage to provide a screen grid of variable diameter. One efiect of this composite structure is the reduction of the relativelyhigh' space current and relatively high i-nfluenoes 'the platecurrent and transconductance and-to that extent enters into the problem cit-producingcharacteristics of desired shape.

a An example of such construction applied to the reduction oftransconductance at the low mu area of the-cathode is shown in Fig. 3. .In the diagram, the cathode 2, control grid G1 and plate P 'have-s'ubstantially the same construction and arrangement as is illustrated in Fig. 1, but the screen grid-G2 is a helical winding of conical 5 for'nifl The larger diameter portion of the screen grid G2 lies between the plate P and the more widely spaced turns of the control grid winding G1, thus reducing the accelerating action of the screen grid at the portion of the space current path over which the control grid exercises a lesser control of space current flow.

The desired variation in control at difierent parts of the electron stream may be effected when the controlgrid of'non-uniformpitch takes other forms than the tone he'r'ein illustrated and de-H scribed.

In my aforementioned copending application I have described and claimed embodimentsot 7 7 equipotential cathode, a control grid comprising 10 the present invention in which a control grid of non-uniform pitch takes the forms, respectively, 5

of a plurality of sections each of uniform; but of different pitch, and a grid having. turns of. uniform pitch but from which one or more of the turns are missing. Other variations in construction which are effective to secure-operation in aC-y' cordance with the present inventionwill occur to those familiar with the design and: operation- It is therefore to belmderr stood that the term non-uniform pitch'as em-' ployed-in the following claims .is 'not restricted to; a progressive variationgin the pitch of vacuum tubes.

or-spacing of the turns of agrid winding.;;; i e

. While the invention been des plied to a known type o f tetrode,itwillbe apparent that itisapplicableto various types of tubes;

which mayor may not include electrodes .addh

transconductance is meant theratio-of theehange,

in thecurrent in the circuit of an: electrode to the chan e in the-v l a e o ano e e e tr de. under the condition that all other yoltages rem n u e By mu-ia r s m an th ratio of the change in one electrode voltage to a change in the other electrode voltage, under the wrre t r me-i 1 condit on th t; a specified qh n h V 1 r .Ielgim r; '1.;An electron discharge device comprising an equipotential, cathode, a; control Lgrid' having :a

winding of non-uniform pitch and exercising different rates of control over-parts ofv the relec'r, tron stream established at .difierentportions; of said cathode, and a plate, a screen Jgridifbetween said control grid and plate, the .diametenDfjhe said'screen gridbeing greatestlin .thatgpartioi,

the electronstream over which said control grid exercisestheleastrate of control; I 2. An electron discharge.-..devicecomprising an zequipotential cathode, a control grid-exercising a:

lesser rate of control over the electron stream established from one portion of the cathode-than.

it-exercises over the electron stream from other 3. A screen; grid tube having variable factor,.a cathode, an anode, a controlegrid' constructed .to-exercise lesserand. greater rate-s of control ov'er parts of the electron stream, and a screen grid comprisinga windingv whichvaries indiameter irom point to point along the winding, the, larger .diameter section ofv the screen grid being,positionedadjacent a portion of the. control gridexercising saidlesser rate of control.

4; An electrondischarge tube comprising an equipotential cathode, a control grid comprising a helical winding. having a pitch which varies progressively from one end thereof to another. a screen grid and a plate, said screen grid comprising a helical winding which progressively increases in diameter from point: to g pointsalong said windingand is mounted ,with;-its-- greatest diameter adjacent the more open end of. said 1;;cpntrol grid winding. r

5. electron discharge tube comprising an a -helical winding having a pitch which varies "progressively from one end thereof to another, a screen gridand a plate, said screen grid having substantially'the form of a truncated cone, the portion of said cone having thewidest diameter 15 being. disposed-adjacent the portions of the contro l "grid winding having the largest pitch whereby there is secured ireductionof the relatively high space current and relatively high transconductance at a portion of the space current path 20 h e. the m rie qr QW;-;; 1 1 I electron discharge tub comprisin -a crlindrical equipotential cathode, a grid nea h c w inapfgn n-umiorm-n r nd n d c ax a wi sa .catho aasecongi 5. ridsur o d nd w xielwiih ai 1fir .g;ri .i-v and comprising a helical windingwhich variesin; iame er, om Point qp pt. e enese ndi w 3+ QT IYQ r i m r i -I lfi with? portion of said first grid n ch g or ager oi;

pitch and a tubular plate surrounding and PC0115 axial with said second grid. 5 V

'7. An electron discharge tube comprisi 'g a ey lindrical equipotential cathode, a grid surround ing and coaxial withsaid cathode 5d a e w ngi w i incr a es t l P 39 7 gressively'from one end to them; er, .a second I grid substantially coextensive withsa'id and comprising a helicalfwin'ding'iof pitch and progressively increasing diameter 1min one end to the other and positioned with end adjacent the end'ofsa'idilrst end we pitch of said first gridis greatest, ame plate surrounding an 'coak'ial'r withs'aid grid. Y 7 8. Anelec'tron discharge'devi mprisln'g a cylindrical i eduipot ential cathode, a tukiillalfpl atf concentric with said "cathode, Iandtwd concentric gridsinterposed between said cathodean'd said! plate, one or said gli'ds exerting different a control ohfelectron streams ironing en tions of said cathode, and theotherhaviii por tions" spaced froin' Said first" "grid at fdifitahesf in creasing vviththe e'xtentf'of 'decre' xerteaby tfilfir stgiidl .I I h l9; A vacuum tube ":eompnsm a cathode, a. scfhgiid, ands; plate, df,.aCofitfo1 tioned between said cathode,andplate'andlhav ing a winding of non-uniform pitc'hlanjd exercise.

ing at different points along. said cathode fdiffe'rl i e01;

entrat'es ofcontrolfioverjjparts ofjthe electr n stream? between. said 1 cathode and "plate,f aid screen gridbeing conical and positioned'coa'xially of said cathode'lwith itslargerportion in rgis grid, whereby said screen grid exercises a lesser. I accelerating action. upon the electronstream at,

those points on the cathode atswhich the control action of said control grid is less; j

try with the less eifective portionsof. saidfcontrgl 65-; 

